The present invention relates to an assembly of an operation knob and a casing for a switch used in a push button switch, a slide switch etc. and a fabrication method thereof.
The conventional configuration of an assembly of an operation knob and a casing for a push button switch will be explained with reference to FIGS. 4 and 5. FIG. 4 is a sectional view in an exploded state and FIG. 5 is a sectional view in an assembled state.
As shown in FIG. 5, an operation knob 21 for a push button switch is disposed so as to be able to slide upward and downward with respect to a casing 22. The operation knob 21 is intended to be prevented from coming out of the casing 22 by means of a not-shown come-out preventing means. Supposing that the operation knob 21 and the casing 22 have the widths A and B as shown in FIG. 4, respectively, a guide clearance C (=Bxe2x88x92A) necessary for sliding the operation knob freely is provided between the knob and the casing. When the operation knob 21 is pushed, a not-shown switch disposed beneath the operation knob 21 is turned on or off.
However, although the guide clearance is provided in order to slide the operation knob 21, the operation knob 21 wobbles after being assembled due to the guide clearance provided between the operation knob 21 and the casing 22 of the push button switch. This wobble is caused by the crossing of the parts, the leaves of the die etc. For example, in the prior art, such a guide clearance is 0.2 mm at the minimum. Conventionally, the length of the knob guide portion L of the operation knob 21 is made longer in order to reduce such a wobble by using the knob actually touched by a hand. As a result, the length of the casing 22 for housing the operation knob 21 also becomes longer and there arises a problem that the size of the push button switch becomes large.
The present invention has been made in order to obviate the aforesaid problem and an object of the invention is to provide an assembly of an operation knob and a casing for a switch and a fabrication method thereof which suppresses the wobble as small as possible by forming a guide clearance between the operation knob and the casing for housing the operation knob by using the heat contraction or heat shrinkage at the time of a molding process thereof so that the operation knob can be downsized and so the assembly of the operation knob and the casing can be miniaturized as compared with the conventional ones.
In order to attain the aforesaid object, the gist of the invention claimed resides in a method of fabricating an assembly of an operation knob and a casing for a switch which is characterized in that the operation knob and the casing for guiding movement of the operation knob are formed by a two-shot molding method by using composite resins, and the operation knob and the casing are separated from each other after being molded.
The gist of the invention further resides in the casing including a guide portion for guiding the operation knob, and a guide clearance being formed between the operation knob and the guide portion of the casing when the composite resins heat-contract at the time of the molding.
The gist of the invention further resides in a heat contraction ratio of the material forming the casing being larger than a heat contraction ratio of the material forming the operation knob.
The gist of the invention further resides in the operation knob being integrally formed with the casing after being assembled so that the operation knob closes an opening portion of the casing which is disposed to move freely, and then the operation knob and the casing are separated from each other.
The gist of the invention also resides in an assembly of an operation knob and a casing for a switch which is arranged in a manner that the operation knob and the casing for guiding movement of the operation knob are formed by a two-shot molding method by using composite resins, and the operation knob and the casing are separated from each other after being molded.
The gist of the invention further resides in the casing including a guide portion for guiding the operation knob, and a guide clearance being formed between the operation knob and the guide portion of the casing when the composite resins heat-contract at the time of the molding.
The gist of the invention further resides in a heat contraction ratio of the material forming the casing being larger than a heat contraction ratio of the material forming the operation knob.
Thus, according to the invention recited, the operation knob and the casing for guiding movement of the operation knob are formed by the two-shot molding method by using the composite resins of the same material or different materials, and the operation knob and the casing are separated from each other after being molded.
Additionally, according to the invention recited, after the assembling process, the guide clearance can be formed between the operation knob and the guide portion of the casing due to the heat contraction of the composite resins at the time of the molding. Thus, the guide clearance can allow the operation knob to move smoothly when the operation knob is operated.
Additionally, according to the invention recited, since the heat contraction ratio of the material forming the casing is larger than that of the material forming the operation knob, the guide clearance used at the time of moving the operation knob can be formed due to the difference of the heat contraction ratios therebetween.
Additionally, according to the invention recited, the operation knob is integrally formed with the casing after being assembled so that the operation knob closes the opening portion of the casing which is disposed to move freely, and thereafter the operation knob and the casing are separated from each other.
Additionally, according to the invention recited, due to the heat contraction caused at the time of forming the operation knob and the casing for guiding the operation knob by the composite resins by using the two-shot molding process, the necessary guide clearance is formed between the operation knob and the casing after being assembled. The guide clearance allows the operation knob to move.
Additionally, according to the invention recited, the guide clearance is formed due to the heat contraction between the operation knob and the guide portion of the casing and so the operation knob can be allowed to move.
Additionally, according to the invention recited, since the heat contraction ratio of the material forming the casing is larger that that of the material forming the operation knob, the functions described above can be obtained.